1. Technical Field:
The present invention relates to ball valves, and, more particularly, to an improved method and apparatus for retracting a spring-loaded ball valve seat from a ball valve member.
2. Discussion of the Prior Art:
Top entry ball valves are well known in the prior art and are widely used to eliminate the need for removing the entire valve assembly from a pipeline for repair and maintenance. Examples of such valves are disclosed in U. S. Pat. Nos. 3,037,378 (Jackson et al); 3,171,431 (Hansen et al); 3,771,545 (Allen); 3,830,465 (Allen); 3,895,776 (Laurens); 3,985,334 (Domyan); 4,266,566 (Kacal et al); 4,388,945 (Johnson et al); 4,390,039 (Johnson et al); in British Pat. No. 1,215,159 (Verdurand et al); and in a 1981 brochure published by Cameron Ball Valve Products of Houston, Texas, entitled "Cameron's New Top Entry Ball Valve". These disclosures, insofar as they serve as general background and examples of the state of the art, are expressly incorporated herein, in their entireties, by this reference.
It has been found desirable to employ spring-loaded valve seats in top entry ball valves in order to provide optimally reliable sealing capability. However, the resulting structures have made it difficult to remove the ball valve member from, and to insert that member into, the valve body. In some valves (for example, see the Kacal et al patent), additional components are incorporated into the ball member and the housing in order to facilitate removal of the ball from the housing. The additional components, however, increase the cost and subject the unit to greater potential for failure.
Another prior art valve (for example see the Verdurand et al British Patent) provides a fork-like tool that can be inserted into the valve housing between the seat and ball and then pivoted to urge the seat away from the ball in opposition to the spring bias force. In order to retain the seat in its retracted position after the tool is removed, a separate latch mechanism is required on the valve body. The latch adds to the cost and the likelihood of failure of the valve assembly.
The two Johnson et al patents describe top entry ball valve assemblies which are intended to overcome the aforementioned disadvantages. In particular, to disassemble the Johnson et al valves one must first remove the bonnet or cover to expose access holes through which the two seats may be contacted by specially-provided cylindrical pins having tapered ends. The pins (two for each seat) are inserted until their cylindrical portions contact the valve seat to force the seat away from the ball member in opposition to the spring bias so that the ball member may be removed from the assembly. Since the pins are longitudinally slidable in the access opening, there is very little precision or control of seat retraction available during the insertion procedure. On the other hand, precision and control are desirable in order to avoid damage to the retainer spring and to permit both sides of the seat to be retracted equally so as to avoid deformation of the seat. In addition, it is impossible to retract the seat in the Johnson et al valves without removing the bonnet or cover. Seat retraction without bonnet removal is a desirable feature, particularly to effect flushing of debris from between the seat and ball without exposing the entire housing interior to what may be a contaminated ambient environment.
The valves disclosed in the Laurens patent and the Cameron brochure overcome the disadvantages associated with the Johnson et al valves. In particular, the seat of the Laurens valve is urged against the ball by means of a spring which is itself urged against the seat by a spacer or load ring held in place by a load screw. The screw has a conical tip and is positionally adjustable to control the bias force applied by the spring in urging the seat against the ball. Retraction of the seat is effected by loosening the screw. The primary disadvantage of this arrangement resides in the fact that the sealing force between the seat and ball depends upon the load screw position. This affects the precision and uniformity of the seal. Moreover, if the two load screws for each seal are differently positioned, the bias force on that seal will differ at diametrically opposite locations. The latter problem affects the operating characteristics of the valve and can result in permanent deformation of the seal when exposed to high fluid pressures in the line.